1. Field of the Invention
The present invention relates to an actuator control system comprising, for example, an electric actuator which allows a displacement member to make linear reciprocating motion under the rotary driving action of a rotary driving source, and a control unit which protects the rotary driving source for driving the electric actuator.
2. Description of the Related Art
A transport means such as an actuator has been hitherto used, for example, in order to transport a workpiece.
An electric actuator concerning the conventional technique is shown in FIGS. 63 and 64 (see, for example, Japanese Laid-Open Patent Publication No. 11-30234).
The electric actuator 1 concerning the conventional technique has a slider 4 which is displaceable along a recess 3 of a frame 2, and a screw shaft 6 which is driven by an unillustrated motor and which is screwed to a nut member 5 that is detachable with respect to the slider 4. Screw shaft support members 7a, 7b, which rotatably support the screw shaft 6, are provided at both ends of the screw shaft 6 respectively. The screw shaft support members 7a, 7b are attached to an upper surface 8 of the frame 2.
In general, when an installation type industrial robot is used, a base is fixed by bolts or the like. When any excessive pressing action or some kind of collision occurs at the forward end of the robot due to an error in the interlock or the like, the operation of the robot is stopped by detecting an overcurrent. That is, the robot and the workpiece are mainly prevented from being destroyed by detecting the overcurrent in the installation type industrial robot, and positional deviation of the robot itself is not taken into consideration.
In view of the above, Japanese Laid-Open Patent Publication No. 2002-66969 discloses a technical concept which is directed to prevent an automatic or unmanned transport vehicle from floating even when a forward end of a robot arm is subjected to excessive pressing action or collision with respect to any equipment.
That is, Japanese Laid-Open Patent Publication No. 2002-66969 discloses a control apparatus which executes the operation for limiting the current for a servo motor for driving the joint of the robot arm when the limit value of the joint torque applied to the joint of the robot arm satisfies a predetermined value when the forward end of the robot arm is moved in response to the control of the attitude and the position with respect to the forward end of the robot arm.
However, when the electric actuator, according to the conventional technique disclosed in Japanese Laid-Open Patent Publication No. 11-30234 as described above, is applied, for example, to the pressing operation for the workpiece, for example, at any intermediate position between one stroke end and the other stroke end in accordance with the back and forth movement performed similarly to a piston rod of a fluid pressure cylinder without using any complicated control apparatus or the like, the durability of the electric actuator is deteriorated, because the shock or impact, which is caused upon abutment against the workpiece, is transmitted to the screw shaft or the like via the slider.
Further, when the technical concept disclosed in the Japanese Laid-Open Patent Publication No. 2002-66969 is applied, for example, to an electric actuator for converting the rotary motion of a motor into the rectilinear motion of a slider or the like, it is necessary to provide a detector such as an encoder and a resolver as well as a control circuit in order to control, for example, the position and the operation speed of the slider, in which the production cost becomes expensive.